1. Field of the Invention
The invention relates to an apparatus and method operable to detect the presence of cracks in a structure.
2. Description of Related Prior Art
U.S. Pat. No. 4,484,132 shows a metal structure (P) covered with an insulating substrate (21) in FIG. 4. Electrically-conducting lines (22) are formed across the substrate (21). The lines (22) are a combination of electrically conductive particles suspended in a flowable material. The lines (22) are applied with a pen or syringe, shown in FIG. 10. After being applied to the substrate (21), the lines (22) cure and dry out. A second insulating layer (23) is applied over the lines (22). When the structure (P) cracks, the substrate (21) and lines (22) adjacent to the crack will also fracture, resulting in a change in voltage across at least one of the lines (22).